Use a stack-based approach to handle operator precedence, where multiplication and division are evaluated immediately while addition and subtraction push values onto the stack for deferred summation. Parse the string left-to-right, tracking the current number and the last seen operator to decide how to process each token. Finally, sum all values remaining on the stack to produce the result.
Pro tip: Mention edge cases upfront — such as multiple spaces, large numbers, and division truncating toward zero (not just floor division) — to signal production-level thinking. Noting that Python's integer division '//' truncates toward negative infinity while the problem requires truncation toward zero shows deep language awareness.
Confirm input constraints: only non-negative integers, operators (+, -, *, /), spaces, no parentheses, and integer division truncates toward zero. Ask about empty strings, single numbers, and division by zero handling.
Explain that a stack elegantly handles operator precedence by immediately computing * and / results and pushing them, while + and - push the signed number for later summation. This avoids building a full expression tree.
Iterate through the string character by character, accumulating digit characters into a current number and acting on the previous operator when a new operator or end-of-string is encountered. Use int(a / b) instead of a // b to ensure truncation toward zero.
For '+' push the current number, for '-' push its negation, for '*' pop the top and push the product, and for '/' pop the top and push int(top / current). Initialize the last operator as '+' to correctly handle the first number.
Sum all values on the stack and return the total. State that time complexity is O(n) for a single pass and space complexity is O(n) in the worst case due to the stack storing all operands.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.